Composite film support

ABSTRACT

A composite film support for photographic material and the like consists of two hydrophobic layers, one of which is comprised of at least 1% by dry weight of black pigment dispersed in a cellulose ester binder and the other is comprised of at least about 10% by dry weight of white pigment dispersed in a cellulose ester binder plasticized with an isocyanate modified lowmolecular-weight polyester. The two layers are in strongly adhering intimate contact at their interface due to the use of low boiling solvents for forming the coating compositions from which both are cast together with the sequence of application in which the second layer is cast upon the first while the first still contains a substantial amount of low boiling solvent and is thus in a relatively soft but nonflowable condition. The resultant film support can carry a light-sensitive silver halide emulsion layer, an image-receiving layer for use in known silver complex diffusion transfer process, a combination of two such layers, or other photographic layers.

United States Patent [72] Inventors Lodewijk Felix De Keyser Mortsel;

Joseph Antoine Herbots, Edegem; Robrecht Julius Thiers, Brasschaat, all of Belgium [21 1 Appl. No. 753,055

[22] Filed Aug. 16, 1968 [45] Patented Dec. 21, 1971 [73] Assignee Gavert-Agla NV Mortsel, Belgium [32] Priority Aug. 16, 1967 [33] Great Britain [31] 37,763/67 [54] COMPOSITE FILM SUPPORT 4 Claims, No'Drawings 96/84, 96/76, 96/87, 117/85, 1 17/144 [51] Int. Cl B32h 23/20 [50] Field of Search... 96/76, 87,

XXXXXXXXXXXX XXXXXXXXXXX Primary ExaminerWilliam D. Martin Assistant ExaminerM. R. Lusignan Attorney-William J. Daniel ABSTRACT: A composite film support for photographic material and the like consists of two hydrophobic layers, one of which is comprised of at least 1% by dry weight of black pigment dispersed in a cellulose ester binder and the other is comprised of at least about 10% by dry weight of white pigment dispersed in a cellulose ester binder plasticized with an isocyanate modified low-molecular-weight polyester. The two layers are in strongly adhering intimate contact at their interface due to the use of low boiling solvents for forming the coating compositions from which both are cast together with the sequence of application in which the second layer is cast upon the first while the first still contains a substantial amount of low boiling solvent and is thus in a relatively soft but nonfiowable condition. The resultant film support can carry a light-sensitive silver halide emulsion layer, an image-receiving layer for use in known silver complex diffusion transfer process, a combination of two such layers, or other photographic layers.

GELATINE SILVER HAL/DE EMULSION LAYER GELATINE SUBBING LAYER CELLULOSE TRIACETATE 4 POLYMER e 770 CELLULOSE TR/ACETATE CARBON BLACK PATENTEI] 05221 an 0 3,829,054

GELAT/NE SILVER HAL/DE EMULSION LAYER GELAT/NE SUBBING LAYER CELLULOSE TRIACETATE' POLYMER N0 XXXXXXXXXXXX XXXXXXXXXXX 1 CELLULOSE TRIACETATE o CARBON BLACK PAPER SUPPORT BAR Y TA COATING LAYER CONTAIN/N6 DEVELOPMENT NUCLEI DEVELOP/N6 SOLUTION GELAT/NE TOP LAYER mm w\\\\\\\\\ 1 GELAT/NE SILVER HAL/DE EMULSION LAYER GELATINE SUBBING LAYER r CELLULOSE TRIACETATE +POLYMER0 TiO .xxxxxxxxxxxxxxx xxxxxxxxx g CELLULOSE TRIACETATE+CARBON BLACK COMPOSITE FILM SUPPORT The present invention relates to a composite film consisting of a black pigmented layer and a white pigmented layer.

The composite film according to the present invention consists of two hydrophobic layers, which are successively cast from a dispersion in low boiling solvents, the second layer being applied when the first layer still contains a substantial amount of low boiling solvent or solvents for the hydrophobic film-forming binder thereof, one of said layers being a blackpigmented cellulose ester layer and the other being a whitepigmented cellulose ester layer.

Such a film is especially suitable as the support of a photographic material, particularly ofa photographic material for use in producing images according to the generally known silver complex diffusion transfer process. Such a photographic material may be a light-sensitive material comprising a highsensitive silver halide emulsion layer, the photographic material being suitable for exposure in a cassette as commonly used for X-ray material or in a camera as applied for the production of positive continuous-tone images by diffusion transfer according to the method, the principles of which are described in A new one step photographic process" E. H. Land-Journal of the Optical Society of America-Vol. 37- Feb. l947-No. 2, p. 6l-77.

lt would be interesting if the sandwich formed by the lightsensitive and the image-receiving layers could be removed out of the camera or the cassette after the imagewise exposure of the light-sensitive layer, and that the development of the negative image as well as the positive image formation by diffusion transfer could take place outside the'camera. In that case the construction of the exposure unit could be simplified thoroughly.

When doing so it is advantageous and often even necessary, however, that the light-sensitive layer be protected from environmental light as long as the processing period is not completed. Up to now no solutions have been proposed, which are satisfactory in all respects. A black paper sheet provided with a white pigmented gelation layer as support for the silver halide emulsion layer has the disadvantages of being expensive and of having a rough surface. The light-sensitive material according to the present invention provides a very simple and elegant solution for the above problem.

Such a light-sensitive material comprises a light-sensitive silver halide emulsion layer and a hydrophobic film support, said support being a composite film of two hydrophobic layers, which are successively cast from dispersions in low boiling solvents, the second layer being applied when the first layer still contains a substantial amount of low boiling solvent or solvents for the hydrophobic film-forming binder thereof, one of said layers being a black-pigmented cellulose ester layer and the other being a white-pigmented cellulose ester layer, the light-sensitive silver halide emulsion layer being applied to the side of the white-pigmented layer.

According to a particular embodiment the present invention relates to such a photographic light-sensitive material comprising moreover a diffusion transfer image-receiving layer so that it forms a so-called multilayer material.

The present invention also relates to a process for the manufacture of images by means of the silver complex diffusion transfer process according to which a light-sensitive material according to the present invention is exposed to am imagewise modified pattern of actinic radiation, and in the presence of a processing liquid, a developing substance, a complexing agent for silver halide, and alkali, and is kept in contact with an image-receiving layer in view of the development of a negative image in the silver halide emulsion layer and of the subsequent image-formation by diffusion transfer.

According to a preferred embodiment the present invention relates to such a method according to which a light-sensitive material carrying a silver halide emulsion layer with camera sensitivity or of the type as used for the registration of an X- ray pattern or a pattern of radioactive radiation, is image-wise exposed while present in a camera or in a cassette protecting it against the actinic environmental light, and thereafter while being in contact with an image-receiving layer and while actinic light is screened off from the front side of the light-sensitive layer, is brought outside of the camera or the cassette, so that the development of the silver halide emulsion layer and the further processing as described above can be carried out.

The said inhibition for actinic light to reach the light-sensitive layer from the front side can be realized in different ways as detailedly described hereinafter. A very interesting way is to use an image-receiving material, the support of which is a composite film support according to the present invention consisting of a black-pigmented cellulose ester layer and a white-pigmented cellulose ester layer. Development nuclei may be applied on top of the white pigmented layer. Such an image-receiving material offers the advantages of providing a white background for the diffusion transfer image and of transmitting no substantial amount of actinic light, whereby the sandwich of the light-sensitive and the image-receiving material can be removed out of the camera for development and transfer image formation in actinic light immediately after said sandwich has been formed. Thus, the present invention also relates to an image-receiving material described in this paragraph and to a method of producing diffusion transfer images, wherein such an image-receiving material is used, occasionally together with a light-sensitive material having a same type of support.

The hydrophobic film according to the invention is a composite film of two difi'erent hydrophobic cellulose ester layers, which are successively cast from dispersions in low boiling solvents. It is particularly advantageous to pour the dispersion for the production of the second layer onto the hydrophobic base layer at the time when the latter, after having been cast from dispersion, just has attained a state of nascent stability of form, i.e. when it is in half solid condition and no longer subject to deformation by slight external forces, although it still contains a substantial amount of low boiling solvent or solvent mixture for the hydrophobic cellulose ester film forming binder thereof. Particularly good adhesion of the two hydrophobic cellulose ester layers constituting the composite film is obtained in this manner. We believe that such adhesion is produced by the fact that the colloidal chemical state of the base layer at this particular period of its formation permits the newly poured layer to combine favorable with the hydrophobic cellulose ester material of the base, but prevents excessive penetration of the low boiling solvent or solvents of the dispersion into the base, so that the base layer itself does not dissolve or soften sufficiently to be injured.

Throughout the specification by the term low boiling solvents" are understood all known solvents for cellulose esters boiling below l00 C. among which the most interesting are methylene chloride, 1,2-dichloroethane, carbon tetrachloride, acetone, methanol and ethanol.

In a very convenient and most preferred embodiment of the invention the black-pigmented cellulose ester layer is a hydrophobic cellulose ester layer pigmented with finely divided carbon black in a concentration between 1 and 5 percent by weight with respect to the total weight of solid material in the black-pigmented layer. In order to disperse carbon black in the black-pigmented layer of the composite film support there can be started, e.g., from a concentrated carbon black suspension in a dilute solution of a cellulose ester in low boiling solvent or solvents. For the preparation of this concentrated suspension, e.g., a mixture of equal parts by weight of carbon black and of a hydrophobic cellulose ester in a certain amount of low boiling solvent or mixture of low boiling solvents for the cellulose ester is ball milled for some time, till a stable and still liquid suspension is obtained. This concentrated suspension can be diluted then with a solution of the same cellulose ester and the necessary amount of plasticizer in the same low boiling organic solvent, till the desired degree of blackness and viscosity is obtained. When the mass contains at least 2 percent of carbon black based on the total amount of solid matter, the films cast from it, when they possess a thickness of about 100 in most cases are sufficiently opaque to actinic light for the purpose of the invention. If the thickness is less than lp., the content of carbon black, of course, must be increased to make the film sufficiently opaque. These figures are moreover dependent on the nature of the carbon black used and on its degree of dispersion. The smaller the size of the carbon black particles, the less carbon black has to be used. ln order to be suitable for the purpose of the invention, the optical density of the black-pigmented layer measured in transmission should amount to about 8.

For coating the white-pigmented layer there can he proceeded in an analogous way. A hydrophobic cellulose ester layer is pigmented with a known finely divided white pigment such as titanium dioxide, barium sulfate, zinc white and lead white. These pigments are dispersed in the cellulose ester coating composition, containing the necessary amount of known plasticizer for the cellulose ester, in a concentration between l0 and 55 percent by weight with respect to the weight of solid material in the white-pigmented layer. The proper concentration will depend on the particular white pigment used and on the degree of light reflection desired. When the concentration of white pigment in the hydrophobic cellulose ester layer exceeds about 25 percent by weight, and depending on the particular white pigment used, the layer coated therewith would be much too brittle, even if a normal amount of known plasticizer for the cellulose ester was added thereto. in order to obviate this inconvenience, the hydrophobic binder of the white-pigmented layer in that case is formed from a mixture of a hydrophobic cellulose ester, occasionally comprising a plasticizer therefor, and of a compatible hydrophobic polymeric material as described below. This hydrophobic polymeric material acts as a polymeric plasticizer for the white-pigmented cellulose ester layer or as an additional plasticizer when a known plasticizer for the cellulose ester is also present.

The white pigmented mass can also be prepared by ball milling. For that purpose the white pigment, e.g. titanium dioxide. together with an amount of cellulose ester and low boiling solvent is ground for some time. The stable suspension obtained is then intimately mixed with a solution of the same hydrophobic cellulose ester occasionally containing an appropriate amount of known plasticizer therefor. If need be, the necessary amount of dissolved hydrophobic polymeric material is admixed to the white mass obtained, and subsequently the suspension is diluted with the necessary amount of low boiling solvent, till the desired viscosity is attained.

According to another method the white pigment is dispersed in a solution of the polymeric material. If need be, a dispersion agent can be added to the mass. Thereupon a solution of the polymeric material and of cellulose ester and occasionally of plasticizer is admixed, till they are present in the desired proportion.

When the mass contains more than l0 percent of white pigment based on the total amount of solid matter, white films can be cast therewith on a black support so that the composite films formed reflect at least 70 percent of the incident light at the white side when a thin silver halide emulsion layer is used. With concentrations of white pigment above 30 percent by weight, even light reflections of even more than 85 percent can be obtained. This reflection of light results in a higher practical sensitivity of the light-sensitive material.

The black-pigmented cellulose ester layer has a thickness varying preferably between 50 and l00p., whereas the thickness of the white-pigmented layer varies preferably between and 50p. so that in most cases the total thickness of the composite support is comprised between 60 and l50u.

The usual hydrophobic cellulose esters are suitable for the black-pigmented layer as well as for the white-pigmented layer, i.e. cellulose triacetate, cellulose diacetate, cellulose nitrate, cellulose propionate, cellulose butyrate, and mixed esters such as cellulose acetopropionate. Further it is not necessary that the same hydrophobic cellulose ester be used for the black-pigmented and for the white-pigmented layer.

The known additives such as plasticizers and, if necessary, stabilizers may be added to both layers of the composite film support. As said hereinbefore, it would suffice theoretically to use as binder in the white-pigmented layer only one hydrophobic cellulose ester, which is normally plastified, e.g. with triphenyl phosphate. Whengreat concentrations of white pigment are added, necessary to obtain a high reflection of incident light during a photographic exposure, too much a brittle layer would be obtained with cellulose ester as the sole binder. This can be remedied by adding to 4 parts by weight of a hydrophobic polymeric material as hereinafter defined for each part by weight of cellulose ester. This procedure confers an extraordinary flexibility to the white-pigmented layer.

For forming the white-pigmented layer, in the description also called the flexible layer, there is added to the solution of cellulose ester a solution of a hydrophobic polymeric material, which is compatible therewith, especially in the case of a concentration of white pigment larger than about 25 percent by weight. This polymeric material may be a low-molecularweight polyester, which has been modified with an aromatic or aliphatic diisocyanate. The low-molecular-weight polyester may be obtained by reaction of an aliphatic diol of 2 to l0 carbon atoms or of a mixture of such diols with an aliphatic dicarboxylic acid of at most 10 carbon atoms. The tenn aliphatic diol must be taken in its broadest sense so that it also comprises aliphatic diols containing hetero atoms in the chain as is the case in dialkanolamines such as diethanolamine. Very good results are attained with polyesters of ethylene glycol and adipic acid or of ethylene glycol, diethanolamine, and adipic acid with a molecular weight of about 2,000 to 7,000. These low-molecular-weight polyesters are modified with aro- -matic or aliphatic diisocyanates, such as 2,4-toluene diisocyanate or hexamethylene diisocyanate, resulting in hydrophobic polymeric materials having molecular weights of about 20,000 to 25,000.

The composition of the flexible layer can vary within wide limits. The best results, however, are attained when it contains for each part by weight of cellulose ester about 15 to 4 parts by weight of polymeric material. By application of this broad ratio of products the composite film, which is finally obtained and which is to be used as support for a further layer or layers, confers a high degree of flexibility to the photographic material according to the present invention.

When manufacturing the composite film to be used as support for the photographic material according to the present invention, the black-pigmented layer need not necessarily be cast first, before the coating composition for the white-pigmented layer is cast on top thereof. In practice, the reversed order will be followed in most cases. First a dispersion of the white pigmented mixture of cellulose ester and occasionally of polymeric material is cast onto the rotating metal drum or onto the endless metal belt of the film-casting machine, and then on top of the partially dried film a black pigmented dispersion of cellulose ester comprising known additives such as plasticizers is cast. After drying, the composite film is stripped from the casting machine in a known way and is then further dried, whereafter it is ready for receiving one or more other layers for the manufacture of a photographic material according to the present invention.

A firm adherence between the black-pigmented layer and the white-pigmented flexible layer is obtained since the solvent of the secondly cast layer will realize an intimate junction with the still weak layer cast first.

A composite film support as described possesses many advantages for the photographic material according to the invention. Such composite film support is completely impermeable to water and thus also to the developing liquid, which in a diffusion transfer process is needed for the development of the latent image in the silver halide emulsion layer and also serves as medium that makes possible the diffusion of the nonexposed and complexed silver halide to the image-receiving layer. As a result of this impermeability no developing liquid and no diffusion silver halide is lost by penetration into the support.

Since normally the white-pigmented flexible layer is coated first on the casting machine followed by the black-pigmented layer on top thereof, the surface of the white-pigmented layer is especially smooth and even. In any case this surface will be much smoother than it would be when common paper was used as support, even when this paper would be provided with a covering layer. To this smoother surface far more uniform layers can be applied, thus resulting in a more intimate contact between the light-sensitive layer and the image-receiving layer during the diffusion transfer step and resulting in the production or a more compact deposit of diffusion transfer silver.

Such a negative material is practically opaque when in contact with an image-receiving material having no transparent support since the black layer prevents the penetration of light almost completely. A consequence of the presence of a white layer, when thin silver halide emulsion layers are used, is an enhanced light reflection during the exposure stage. Measurements proved that 70 percent to 95 percent of the incident light in the photographic camera was reflected, which results in a sharp increase of the light-sensitivity of the negative material.

In the preparation of the photographic light-sensitive material for use according to the silver complex diffusion transfer process any silver halide emulsion layer can be used, which is characterized by a sufficiently rapid development of the exposed silver halide and by a sufficiently rapid complexing of the nonexposed silver halide to meet the requirements of the diffusion transfer process.

According to a preferred embodiment the silver halide emulsion layer is a rather high-sensitive emulsion layer, which has to be protected from environmental light, and which is suitable for making exposures in a camera or for being used for the direct or indirect recording by means of a fluorescent screen of an X-ray pattern or a pattern of a radioactive radiation as described in Dutch Pat. application No. 6,803,940.

For recording by means of a camera, use is preferably made of silver halide emulsion layers having a rather soft gradation and which consequently are suitable for making continuoustone reproductions. The emulsion layers may be of the type for the production of black-and-white diffusion transfer copies as well as for the production of color diffusion transfer images. For more details reference can be made to the above-mentioned publication of E. H. Land.

The light-sensitive emulsion layer is applied to the whitepigmented layer of the composite film support occasionally after (a) suitable subbing layer(s) and/or one or more further layers have been applied.

The light-sensitive material may be provided with a waterpermeable layer on top of the silver halide emulsion layer. This may be a layer of a metal alginate insoluble in water, as known from the United Kingdom Pat. No. 988,955, or a layer of the chromium salt of carboxymethylcellulose occasionally together with a water-soluble metal alginate as known from our United Kingdom Pat. No. 998,956. Preferably, however, an unhardened or slightly hardened layer is applied on top of the silver halide emulsion layer. Therefore reference can be made to the United Kingdom Pat. Nos. 1,054,252, 1,054,253 and 1,057,273.

For carrying out the method of the present invention the image-receiving layer for use together with the said light-sensitive material may form part of a usual separate image-receiving material generally known in the art. Such a material comprises a suitable support, e.g. a paper support or a hydrophobic film support, and the image-receiving layer mostly containing (a) substance(s)'for precipitating a silver-containing image from the difi'using complexed silver halide, i.e. the socalled physical and/or chemical development nuclei dispersed in a colloid medium or in an inert matrix, e.g. a silica matrix, applied thereto.

According to a particular embodiment of the present invention, the image-receiving layer containing development nuclei may be applied to the same hydrophobic composite film support, to which the light-sensitive layer has been applied, so that a multilayer material is obtained. The image-receiving layer may be applied first to the support and the light-sensitive layer on top thereof but in most cases after a suitable separating layer has been applied between them. More particulars on such a multilayer material and the processing thereof can be found in the United Kingdom Pat. Nos. 1,006,292 and 1,027,742. The multilayer material may also comprise in reversed order on the support first the light sensitive layer and then the image-receiving layer. At least a stratum containing the diffusion transfer image may be transferred to another sheet but this is not always necessary.

For the production of a diffusion transfer image according to the present invention the photographic light-sensitive material is imagewise exposed and kept in contact with an image-receiving layer in the presence of a processing liquid, a developing compound, a complexing agent, and alkali. After the image formation, in most cases at least a stratum of the image-receiving layer containing the diffusion transfer image is separated from the light-sensitive layer.

The contact between the light-sensitive and the imagereceiving layers need not necessarily begin after the exposure step. In some cases, e.g. when a multilayer material is used, the image-receiving layer is brought earlier in contact with the silver halide emulsion layer.

By the wording contact between" there is not necessarily meant a direct contact but any contact either direct or by means of at least one intermediate water-permeable layer that permits a transfer of processing liquid, of ingredients for carrying out the diffusion transfer image formation, and of complexed silver halide from one layer to the other.

The image-receiving layer is the nuclei-containing layer wherein or whereon the diffusion transfer image is produced. At the separation stage of the light-sensitive layer from the image-receiving layer at least an image-comprising stratum of this latter is separated from the silver halide emulsion layer. According to a particular embodiment the nuclei instead of being incorporated during the preparation step of the imagereceiving layer may be supplied to the image-receiving layer during processing as well, e.g. by the processing liquid incorporating them. For more particulars about this embodiment reference can be made to the United Kingdom Pat. Nos. 1,001,558 and 1,052,022.

The image-receiving material is the whole material comprising the image-receiving layer or to which at least a stratum comprising a diffusion transfer image is transferred.

ln carrying out the method according to the present invention the aqueous processing liquid may be applied to at least one of the light-sensitive and image-receiving materials, preferably to the light-sensitive material alone or to both materials. This supply of processing liquid can occur in any way, e.g. by dipping the material to be wetted in the processing liquid, by means of a roller, by bringing the material in contact with a subject soaked with the processing liquid, by spraying, and by spreading a viscous or nonviscous processing liquid, e.g. contained in a pod.

The necessary ingredients for carrying out the diffusion transfer process, i.e. the developing compounds, the complexing agents of the unexposed silver halide and the alkaline substances can be present in the processing liquid. However, at least one of these ingredients may be incorporated into the photographic material(s) used. For the application of the developing substances in the materials reference can be made to the Dutch Pat. No. 107,251 and the United Kingdom Pat. Nos. 1,012,476, 1,042,477, 1,054,253, 1,057,273, 1,086,510 and 1,093,177. By incorporating all the developing substances into the material(s) used, the processing liquid can be reduced to an alkaline bath that is substantially free from developing substances and that occasionally may comprise a complexing agent for the nonexposed silver halide. By incorporating the alkaline substances and the complexing agent into the materials as well, the diffusion transfer image can be formed by using mere water as a processing liquid. Therefore reference can be made to the United Kingdom Pat. No. 1,013,343. In case of the production of color images in the image-receiving layer, the

necessary compounds have to be present in the materials(s) used and or in the processing liquid.

All other ingredients commonly used in the diffusion transfer process may be incorporated into the material(s) used and/or into the processing liquid, Such ingredients are, e.g., stabilizing agents, hardening agents, preservatives for developing substances, compounds counteracting yellowing, toning agents, antisludge agents, pigments, latices, etc.

All the ingredients used in the processing liquid or in the materials used may be applied in the usual concentrations generally known from the literature.

According to a preferred embodiment of the method of the present invention, a highly light-sensitive material as defined above is imagewise exposed in a camera or in a cassette while being protected against incident environmental light.

In order to be able to carry out the processing step leading to the production of the diffusion transfer image at least for the greater part in actinic light, whereby the processing unit, e.g. the camera itself, can be simplified considerably, also the front side of the exposed silver halide material has to be protected against actinic light before it is taken from the camera, the cassette or other processing unit protecting it against the environmental actinic light. This protection can be performed by pressing an image-receiving material, of which one or more composite layers together do not transmit light (e.g. a material having a same type of composite film support as that used for the light-sensitive material) or to which backside a separate sheet transmitting no light has been applied, against the lightsensitive material before the sandwich thus obtained is exposed to light. Such a separate sheet transmitting no light can be removed later. By using a multilayer material comprising both a light-sensitive silver halide emulsion layer and an image-receiving layer a separate sheet transmitting no light can be brought in firm contact with the multilayer material before the whole is brought in actinic light. This separate sheet can also serve as an auxiliary sheet for separating the light-sensitive layer from the image-receiving layer after the image-formation by diffusion transfer has occurred. Such an auxiliary sheet may contain (a) substance(s) necessary for the produc tion of a diffusion transfer image as described in the United Kingdom Pat. No. 1,027,742.

The processing liquid can be applied in the manner described above just before the sandwich of light-sensitive and image-receiving materials or auxiliary sheet is formed. Then the sandwich can immediately be brought in the actinic environmental light, so that the development of the silver halide emulsion layer and the image formation by diffusion transfer can take place. During this time the light-sensitive layer is protected against actinic light. As an alternative for the application of the processing liquid the latter may be present in a pod contained in the sandwich. By exerting pressure on the sandwich brought in the actinic light, this liquid can be spread, whereupon the development can start.

The following examples illustrate the invention. Schematic representations of the materials obtained in the examples are shown in the drawings wherein P16. 1 represents the material described in examples 1-3 and FIG. 2 represents the materials of examples 4 and 5.

EXAMPLE 1 A polymeric material was prepared by the polycondensation of adipic acid with a mixture of ethylene glycol and diethanolamine to a polyester having a molecular weight of 5,000 to 7,000 and by the reaction of this polyester with 2,4- toluene diisocyanate, whereby a polymeric material is obtained having a molecular weight of about 25,000.

A mixture consisting of 400 g. of titanium dioxide and 60 g. of cellulose triacetate in 880 cc. of a mixture of 90 parts by volume of methylene chloride and parts by volume of ethanol was ball milled for 48 hours. To the white paste obtained a solution of 60 g. of cellulose triacetate in 1,000 cc. of the same solvent mixture was added. To the suspension thus dry, and as soon as the layer had attained a stage of nascent stability or form as explained above, a black-pigmented composition was applied thereto, which was obtained as follows.

A mixture consisting of 1,760 g. of cellulose triacetate, 265 g. of triphenyl phosphate, 2,600 g. of carbon black, and 47.5 liter of a mixture of 10 parts by volume of methylene chloride and ethanol was ball milled for 24 hours. An amount of cc. of the paste thus obtained contains 3.5 percent by weight of cellulose triacetate, 0.5 percent by weight of triphenyl phosphate, and 5.2 percent by weight of carbon black.

12 liter of this black paste was added to 10 liter of a solution of 2,200 g. of cellulose triacetate and 330 g. of triphenyl phosphate in a mixture of 90/ 10 parts by volume of methylene chloride and ethanol. The black-pigmented composition was applied to the still plastic white layer in such a way that after drying, together with the white layer, a composite film of about 1 10y. thickness was obtained. The black layer contained about 2.4 percent by weight of carbon black.

The composite film was then removed from the casting machine and its white side was coated successively with a gelation subbing layer and a high-sensitive gelation silver halide emulsion layer having a soft gradation.

To the back side an antistatic layer can be applied.

The lighbsensitive material thus obtained was very suitable for use in the production of continuous-tone images according to the silver complex diffusion transfer process.

The blackpigmented layer did not transmit a substantial amount of light and the white-pigmented layer possessed a very strong light-reflecting power and a very smooth surface, so that the light-sensitive layer applied thereto was very flat as well, whereby a more uniform and more intimate contact with the image-receiving material was attained.

EXAMPLE 2 Ethylene glycol was polycondensed with adipic acid to a polyester having a molecular weight of about 2,000. This polyester was modified with 2,4-toluene diisocyanate to a polymeric material having a molecular weight of about 20,000.

According to the method described in example 1 a white paste was prepared containing 60.78 percent by weight of 1,2 dichloroethane, 32.80 percent by weight of titanium dioxide and 5.76 percent by weight of the above formed polymeric material. Thereupon 0.66 percent by weight of a photographically inert dispersing agent was admixed. By means of this white paste a series of coating compositions was prepared, all of them containing 40 percent by weight of titanium dioxide, by mixing the white paste with a solution of 22.5 percent by weight of cellulose triacetate and 30 percent by weight of the polymeric material in a mixture of 90/ 10 parts by volume of methylene chloride and ethanol. The additions were done in such a way that in the different coating compositions l, 1.5 2, 3.2 and 6.6 parts by weight of polymeric material were present for each part by weight of cellulose triacetate.

As comparison material also a white paste was taken comprising a cellulose triacetate as a binder.

Before deaerating and coating, the viscosity of all these compositions was adjusted to 25,000 c.p.s. by admixing methylene chloride.

On the endless belt of a film casting machine the white-coating compositions were coated to films, which after drying were 30p. thick. Immediately after coating of the white layer however, a black layer was applied thereto in such a way that after drying the white-black composite film was about 110p. thick. The black-coating composition consisted of 22.5 percent by weight of cellulose triacetate, 3.3 percent by weight of triphenyl phosphate, and 0.75 percent by weight of carbon black in a mixture of 90/10 parts by volume of methylene chloride and ethanol. After drying, the black-pigmented layer contained 2.8 percent by weight of carbon black with respect to the total weight of solid matter in the layer.

The mechanical properties of the composite films are listed in table 1 below.

TABLE 1 Ratio of cellulose triacetate 1ymeric material in the white ayer Total thickness in IL 110 105 105 105 100 125 Tensile strength in lrg./sq. mm 8. 7 9. 8. 8 8. 7 8. 9 7. 3 Elongation at break in percent- 11.0 15.3 14.0 12.8 11. 1 13.5 Folding endurance, number of double folds at:

o R.H 22 90 64 76 95 89 30% R.H 5 86 68 66 80 73 Reflectance of light in percent 84. 3 92 92 92. 5 91. 6 93 1 Comparison material.

The tensile strength and the elongation at break were measured with commercially available apparatus, e.g., an lnstron Tester. The folding endurance was determined with the M'l'l' Folding Endurance Tester described in the American Standard Method for Determining the Brittleness of photographic 'Film"(Pl-l. 1.31-1965).

It appears from the figures of the table that the brittleness of the comparison material is much too large since the number of double folds, which can be made with the material is very low. By admixing polymeric material to the cellulose triacetate in the composition of the white layer, a remarkable amelioration of the number of folds was obtained. With 6.6 parts of polymeric material for each part of cellulose triacetate, the material was flexible, but its surface is too sticky and the material as such was unusable. By providing these materials at the side of the white-pigmented layer successively with a usual gelation subbing layer and a gelation silver halide emulsion layer, light-sensitive materials were obtained, which were very suitable for being used in the silver complex diffusion transfer process.

EXAMPLE 3 To 1,500 kg. of white paste consisting of 475.5 kg. of titanium dioxide and 83.5 kg. of polymeric material as prepared in example 2 in 1,2-dich1oroethane was admixed while stirring a solution of 200 kg. of low viscous cellulose triacetate and 300 kg. of polymeric material of example 2 in 1,900 l. of a 90/10 mixture in parts by volume of methylene chloride and methanol. After mixed thoroughly the white composition was brought to a viscosity of about 20,000 cp. by adding a mixture of 90/10 parts by volume of methylene chloride and ethanol, whereupon the composition was completely deaerated under reduced pressure. Then the coating composition was transformed in a film-casting machine to a film, which after being dried was 30p. thick. The white layer consisted of 45 percent by weight of titanium dioxide and 55 percent by weight of binder mixture (1 part of cellulose triacetate per 1.9 parts of polymeric material). Before the layer became dry, however, a black layer was coated thereon in such a way that the total thickness of the dried composite film amounted to 140 1.. The coating composition for this black layer was obtained by ball milling for 20 hours a mixture of 52 kg. ofcarbon black, 32 kg. of cellulose triacetate, 4.8 kg. of triphenyl phosphate, 828 liter of methylene chloride. and 92 liter of ethanol. One part of this black paste was mixed with 10 parts of a solution of 2 parts of cellulose triacetate and 0.3 parts of triphenyl phosphate in a /10 mixture of methylene chloride and ethanol and the composition obtained was diluted with the same mixture of methylene chloride and ethanol, till a viscosity of 25,000 cp. was measured.

The very flexible white-black support transmitted no sunlight and reflected 94 percent of incident light. By applying at the side of the white-pigmented layer successively a gelatin subbing layer and a silver halide emulsion layer, a light-sensitive material was obtained, which was very suitable in a silver complex diffusion transfer process for bringing the sandwich of the light-sensitive and the image-receiving materials immediately outside the camera in the daylight, in order to allow the development of the light-sensitive material and the image formation by diffusion transfer to take place.

EXAMPLE 4 A light-sensitive material was prepared by coating a whiteblack composite support sheet as described in example l on its white pigmented side successively with a gelatin subbing layer, a high-sensitive (27 DlN) blue-sensitized gelatin silver halide emulsion layer having a very soft gradation in a proportion of the equivalent amount of 2.5 g. of silver nitrate per sq.m., and a gelatin top-layer pro rata of 0.5 g. per sq.m.

An image-receiving material was prepared by hot glazing at its baryta side a baryta-coated paper support substantially transmitting no visible light. Then it was provided with a development nuclei-containing layer from the following composition applied in a proportion of 1 liter per 10 sq.m.

water 825 cc.

gelatin 41 g. 0.2 by weight dispersion of nickel sulphide nuclei in a 10 5 aqueous solution of gelatin 41 cc. 1 5 solution of his(dimethyl-thio-carbamoyl)sulphide in ethanol 82 cc.

12.5 1: aqueous solution of saponine 4 cc. 20 aqueous solution of formaldehyde 2 cc. The following developing solution was used distilled water L000 cc. l-phenyl-3-pyrazolidinonc 1 anhydrous sodium lulfite 75 g. sodium hydroxide 25 g. hydroquinone 16 g. p-monornethylaminophenol sulfate 5 g. potassium bromide l g. anhydrous sodium thiosulfate 8.2 g. ammonium thiosulfate 24.5 g. sodium metlbisulphite 7.3 g.

The pH of this developing solution was l 1.5.

The light-sensitive material was exposed imagewise in a camera to a continuous-tone original and then wetted with the developing solution at the emulsion side only. Then it was brought in contact with the image-receiving material. lmmediately thereafter the sandwich formed by the light-sensitive material and the image eceiving material pressed against each other was brought outside the camera into daylight. Subsequently the development of the light-sensitive material and the image formation by diffusing transfer took place for about 60 sec., whereupon both materials were peeled apart. The image-receiving material showed a high-quality positive continuous-tone reproduction of the original. No fault was observed that could be ascribed to daylight having impinged during processing.

EXAMPLE 5 Ten thousand nine hundred and forty grams of titanium dioxide and 1,640 g. of cellulose triacetate where ball milled for 48 hours in 27.35 liters of a 9 to 1 volume mixture of methylene chloride and ethanol. To the white paste obtained a solution of59 kg. of cellulose triacetate and of) kg. ofdiphenyl phosphate in 240 liters of a 9 to 1 volume mixture of methylene chloride and ethanol were added.

The white-pigmented thoroughly mixed composition which contained 13.5 percent by weight of titanium dioxide with respect to the solid matter present was coated, with a filmcasting machine in such a way that after drying the film produced would have a thickness of about 30 Before the white-pigmented film was completely dry, and as soon as the layer attained a stage of nascent stability of form as explained above, a black-pigmented composition was applied thereto as described in example 1 in such a way that the total thickness of white layer together with the black-pigmented layer amounted to about 90 1..

In the following table the mechanical properties of the composite film obtained are compared with a fully transparent cellulose triacetate film of the same thickness.

These mechanical properties were measured according to the methods described in example 2.

The composite film was then removed from the casting machine. The white-pigmented layer showed a light reflection capacity of 75 percent.

Onto the white side of the composite film was coated successively a gelatin subbing layer and a high-sensitive silver halide emulsion layer having a soft gradation.

The light-sensitive material thus obtained was very suitable for use in the production of continuous tone images according to the silver complex difiusion transfer process.

We claim:

1. A composite film consisting of two hydrophobic layers, which are successively cast from dispersion in low boiling solvents, said layers being in intimate strongly adhering contact at their interface by virtue of penetration of the solvent of the second layer into the first layer prior to substantial hardening thereof, one of the said layers being a black-pigmented cellulose ester layer containing about i to 5 percent by weight of solids of a black pigment and the other layer being a white-pigmented cellulose ester layer plasticized in a weight ratio of about 0.54 per part of said cellulose ester with a low molecu lar weight polyester modified with an aliphatic or aromatic diisocyanate and containing about 10 to 55 percent by weight of solids of a white pigment, said polyester being of an aliphatic diol and an aliphatic dicarboxylic acid containing up to 10 carbon atoms.

2. A composite film according to claim I, wherein the cellulose ester of at least one of the black-pigmented layer and the white-pigmented layer is cellulose triacetate.

3. A composite film according to claim 1, wherein said low molecular weight polyester is selected from the group consisting of a low molecular weight polyester of ethylene glycol and adipic acid and a low-molecular-weight polyester of ethylene glycol, diethanolamine and adipic acid, which polyester has been modified with 2,4-toluene diisocyanatc.

4. A composite film according to claim I, wherein the black-pigmented layer has a thickness varying between 50 and p. and wherein the white-pigmented layer has a thickness varying between l0 and 50p" 1! i t t 

2. A composite film according to claim 1, wherein the cellulose ester of at least one of the black-pigmented layer and the white-pigmented layer is cellulose triacetate.
 3. A composite film according to claim 1, wherein said low molecular weight polyester is selected from the group consisting of a low molecular weight polyester of ethylene glycol and adipic acid and a low-molecular-weight polyester of ethylene glycol, diethanolamine and adipic acid, which polyester has been modified with 2,4-toluene diisocyanate.
 4. A composite film according to claim 1, wherein the black-pigmented layer has a thickness varying between 50 and 100 Mu and wherein the white-pigmented layer has a thickness varying between 10 and 50 Mu . 